Performance Analysis of CSMA/CA protocol in IEEE 802.11 Networks using Backoff mechanism

Performance Analysis of CSMA/CA protocol in IEEE 802.11 Networks using Backoff mechanism

Abstract:

The distributed coordination function (DCF) in the IEEE 802.11 standard for wireless LAN is based on the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) like medium access control protocol. This collision avoidance is implemented by means of backoff procedure which uses a rotating window mechanism. This paper presents a simulation analysis of the slot selection probabilities and the backoff mechanism. The obtained simulations allow us to determine the effective throughput versus offered load for different values of the contention window parameter and the number of the contending stations. The choice of CWmin and CWmax parameters were analyzed.

Introduction:

With the spread of high performance portable computers, data terminals, and devices such as personal digital assistants, Wireless LANs (WLANs) have become an emerging technology for today’s computer and communication industries. They will pay their part in the network architecture as a provider for easy and unconstrained access to the wired infrastructure – an extension of the wired network with a wireless last link to attach the large number of mobile data communication terminals. WLANs are also increasingly being used in the hospitals and university environments in which users are high mobile and may only require moderate bandwidths. WLANs have also been used in environments where cable installation is expensive or impractical. Two organizations have been involved in standardizing the physical layer and the medium access control for WLANs, namely IEEE 802.11 wireless LAN and ETSI HIPERLAN. In this paper we are considering only the IEEE 802.11 MAC (Medium Access Control) layer.
The backoff mechanism has intensively been studied in the literature since the beginning of 70’s. The idea of using the backoff mechanism in the MAC layer of the IEEE 802.11 standard has brought a new interest in such a mechanism. The proper selection of backoff parameters is an essential issue for the network performance. For example, the problem of unequal slot selection probabilities was considered in [3]. Two modified backoff schemes, namely weighted selection probabilities and load adaptive selection were proposed with an increase in the throughput performance and the decrease in the average access delay.


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